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What is the most 'environmentally friendly' way to learn to fly?
As this question indicates, I've been thinking recently about the environmental impact of flying (since when automated cars are the only means of ground transport, aviation will be responsible for most greenhouse emissions).
So, as an amateur, novice pilot, I would like to know which is more environmentally friendly, learning in a glider or learning in a single engine prop (Piper Tomahawk, Cessna and the like)?
At first it seems obvious, the glider doesn't have an engine while the latter does. But if we assume the launch method of the glider is tow rope, this would be powered by a single engine prop, using more fuel than it would if it wasn't towing, plus the climb is the most fuel-expensive part of the flight anyway, leading me to think there might not actually be that much difference.
Clarification on this issue would be greatly appreciated.

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Transportation only accounts for 29% (2017, US) or 14% (2014, world) of greenhouse gas emissions. So your premise that aviation will be responsible for most emissions after cars go electric is far from the truth (perhaps you meant transportation greenhouse gas emissions in particular?). Also, remember that electric cars aren't emission-free unless they're being charged with renewable energy.

As a sidenote, renewable energy is not emission free. It might produce very little emissions, but it is not totally emission free.

Here are some options for flying in an environmentally friendly way:

Use an electric trainer: Since last year the all electric trainer aircraft Pipistrel Alpha Electro has FAA certification. Assuming the batteries are charged with renewable energy, this would mean no greenhouse gas emissions at all (excluding manufacturing). It will probably still take some time until larger all electric aircraft with higher ranges are available, but Airbus has already started research.
Use a glider with a winch: Assuming the winch is powered by renewable energy, this would also result in no greenhouse gas emissions. While winch launches are less common in the US, this might change in the future.

If you use a glider with tow plane, it will depend on how long you can fly with the glider. Assuming good thermals you could stay in the air for quite a while, which would easily be better for the environment than a single engine prop plane. But for training (where you would presumably want many takeoffs and landings), I agree with you that the tow plane would now use more fuel because it has to drag the glider along.

Thanks for the helpful answer. My issue with winch launches, is that most accidents (particularly fatal ones) are associated with them: https://members.gliding.co.uk/library/safety/2018-accident-review/

@Cloud I don't see how the linked document supports your claim when the tow-related incidents described in it outnumber the winch ones. In my, admittedly casual, reading on this topic I've mostly come across link failures, which are a common issue to all types of launches.

winch launches are intense but awesome, enviromental impact is the same of a big truck stopping at an intersection. Anyway, with a 10 min tow on a good day you'll fly 6 hours so really gliders enviromental impact is low.

It's not really clear that Airbus' 'hybrid' research is much more than for marketing. There's not much reason to go 'hybrid' with an airplane, like there is with cars. Airplanes don't stop and go like cars do (at least not in the air.) They just go the whole time until they land. The only real opportunity for regeneration would be braking on the ground and carrying around the extra weight to do that would far outweigh any gains.

As an alternative to the winch launch, how about a self-launching glider with an electric motor?

@reirab Aren't most jetliners already hybrid, though? They use their engines to run electrical generators to provide the plane's electrical power...

@nick012000 But they don't use that electrical power for propulsion. Hybrid means you run a prop with electric power during cruise and only use conventional propulsion for takeoff and climb, where more thrust is needed.

That may be a British problem.  American winches can launch F-14 Tomcats :)

@Cloud During my gliding training, there was extensive awareness and training about Winch launch failures and accidents and I never felt unsafe during them.

@nick012000 Pretty much all gas-powered cars (and nearly all airplanes in general, not just airliners) do that, too, but that doesn't make them 'hybrids.' 'Hybrid' means that it uses stored electrical power to aid in propulsion, not just that the engine also drives a generator to power the non-propulsive electronic systems.

@reirab It would be interesting if they could recover some of their gravitational potential energy as they descend, but while possible in theory, the engineering seems quite insurmountable with our technology. I mean, for a prototype it's as simple as having wind turbines feed a battery as you descend (instead of dissipating the energy as wasted drag), but that's the only easy part :D

@Luaan If you manage your energy right, the gravitational potentially energy you have at altitude is used to continue flying during the descent. Indeed, you typically need to carry at least some amount of power through the descent (at least in powered airplanes.) Pretty much the only times when energy is just being totally wasted is when the spoilers are deployed and during the landing roll-out, where you obviously need to dump a lot of kinetic energy rather quickly. (Of course, there are a few maneuvers that can be done to lose energy, too, such as slip, 360s, s-turns, etc.)

@Cloud how do you determine that from the publication? With appropriate consideration for eventualities, winch launching is not fundamentally unsafe.

By using as much simulator time as possible.

Simulators aren't realistic enough to provide any sort of learning experience though.. right? (At least ones you could purchase for the home)

@Cloud https://aviation.stackexchange.com/q/738/1467

Learnt to fly a solar powered hot air balloon

The UK's International Balloon Fiesta in Bristol is a celebration of all things hot air ballooning, but this year it's taken a big stride into the future. August 6th saw the maiden public flight of the world's first hybrid hot air balloon, which flies by heating regular air from the sun alone.Source

In theory, fly forever with no fuel costs.

Although the question may not be explicit I don't see how this would help OP learn to fly anything like a glider or a Cessna.

Can't help the OP if they're not explicit. How about KSP? Or jumping off a mountain? certified to fly is a different question and none of the answers that should be here would speak to that. #clickbaittitles

@Mazura Or jumping off a mountain? It takes lots of traditional skydives (from some kind of powered flying machine) before you get to that point. But I agree with the statement, the question is about flying/piloting not a specific way of flying.

You could use the Peter Pan method: just think lovely thoughts. :)

The answers by Bianfable are pretty good. I'd add one more option:

Use a powered glider.
There are gliders with a small engine, electric or otherwise. Some look like propeller planes with glider wings, some have a much smaller engine and a retractable or foldable propeller. My favourite example is this one. These can take off under their own power, which is less energy-intense than even a winch start, but they can then still stay aloft without using the engine, provided the weather is suitable. I think they're probably also good for beginners as it's much easier to get out of situations where an unexpected change of wind direction prevents you from making it back to base...

The answer is pretty simple. A foot-launched glider (paraglider, hang-glider or ultralight) launched from a hill has zero emissions from the flight itself. It doesn't get more environmentally friendly than that!

You still have to transport the gliders there, and you will have very limited flight time and low chance for thermal from a hill launch. A winch at an airfield might be more effective, because the gliders are stored there and are manually pushed around the airfield. And it requires less people. Unless all of them walk there or use bicycles, it's another factor.

Flying a hill gives you infinite flight time, limited only by the wind continuing to blow in that direction with an acceptable range of strength, and by daylight since hang-gliders aren't legal for night flying. Fair point about getting there, but that's the same for getting anywhere including going to the shops.

@vsz - Hill launching of a paraglider in the UK usually involves walking up the hill with the glider on your back.  You can soar up and down the ridge for as long as the weather permits, looking for the house thermal to get you high enough to go cross country

@DaveGremlin : with paragliders, sure. But if we are talking about aircraft, in the classical stick+pedals configuration, then it requires more complex transportation.

"which is more environmentally friendly, learning in a glider or learning in a single engine prop (Piper Tomahawk, Cessna and the like)?"
I think you can combine the two. Glider for learning basic stuff in the airport environment and nearby (launching however the local method is, in my area that seems to be tow plane), and then small engine (100 HP) for the longer trips where there is more navigation skills and radio work/electronics (ADS-B Out) required for the controlled airspace/tower  interaction.

I wanted to do this, but this answer suggested otherwise: https://aviation.stackexchange.com/questions/64937/will-dual-learning-in-a-glider-make-my-airplane-learning-safer

I would have drawn the opposite conclusion from that. But I only have powered flight time (900 hours), and none in gliders.  My home airports have both been under Class Bravo Mode C veil, so radio work/transponder has been needed for all flights.  There is a glider field 12 nm west that is outside the Mode C veil, we've stopped in on occasion to have a look at the gliders and watch a towed launch or two.

I learned power flying the mid 70s but didn't take up soaring until the 90s.  In hindsight it would have been beneficial to have learned gliding/soaring first.  However, what I did do back then was do my private in a Cherokee 140 then immediately got checked out in an Aeronca Champ, which pretty much flies like a glider with a noisy vibratey thing in front.

Glider flying procedures are nothing like an "airport environment." Since gliders have no ability to "go around" to abort a landing attempt, and (except for motorized gliders) can't taxi on the ground, you won't learn anything equivalent to "flying circuits" in a powered aircraft at an airport, for example.

@JohnK Hi John, how can I make sure I don't cartwheel / die in a glider? This happens a couple of times a year in the UK... I don't know, flying powered just 'feels' safer to me, (even though I know the statistics say otherwise)

@Cloud  Exposure.  You do anything for a while successfully and the perceived risk declines.   I can tell you one thing.  I you give me the choice of being caught out of gliding distance of the airport in a glider, or the engine going south in my power plane in the same spot, I'll take the glider in a heartbeat.  Although, if I'm over flat landable terrain, neither one is really life threatening with any reasonable level of competence.

The primary source of pollution from single engine propeller airplanes is the avgas used as fuel. Avgas is typically gasoline with tetraethyllead (TEL), a lead-containing additive used to reduce engine knock. The most environmentally friendly way to learn to fly, short of using a fully electric airplane, is to use an engine which supports unleaded automotive gasoline, mogas, natively. For such engines, you will usually need to use gasoline without any ethanol, as it will damage an engine not designed for it.

The lead helps with knock resistance (pre-detonation) at altitude.  Diesel (jet fuel) may be an option for more planes some day https://deltahawk.com/  or https://eps.aero/ Problem is retrofitting it into certified aircraft - the combination of engine and aircraft has to be certified.  I thought I saw 90K to have one installed in my plane, which is somewhat more than a new avgas engine at 50K plus mechanics time to remove & put all the accessories back on and reinstall. Jet fuel around here is a lot more than avgas tho, and the airport where I'm based doesn't carry it.

DA42 (twin) and some versions of DA40 (single) natively have diesel engines and burn Jet-A.

While it's true that getting rid of the need for TEL would be nice, the number of light training aircraft that can run on car gas is quite small compared to those that run on avgas... and they tend to be substantially newer and, thus, significantly more expensive. It will be pretty rare to find an aircraft available to rent for flight training that runs on car gas. You can certainly by new aircraft that run on car gas, but that's probably not something you're going to want to do for primary flight training (unless maybe you're quite wealthy.)

@reirab  Most piston engines run perfectly fine on 91 octane auto fuel and there are STCs for all sorts of them.  The fuel has to be alcohol free, and you have to take some measures against vapour lock (keeping fuel system cool  in hot weather).  My Lyc O-290 is MUCH happier on mogas than 100LL, because it is not able to scavenge the lead level and I have to clean plugs every 15-20 hours.  The only benefit to leaded fuel is valve seat lubrication but newer hard metal valve seats negate this factor.

@CrossRoads Unfortunately, diesel engines (and Jet-A piston engines) are often heavier, which makes them less practical for lightweight introductory aircraft where weight is at a premium.

A significant part of the environmental cost of the airplane is building it in the first place.
That becomes relevant in a crash.  A gentle crash saves the airframe, a rough crash makes you buy another airplane.
Therefore, glider training is an environmental win, because it makes you better trained to gracefully recover from an engine-out situation, giving you a good eye for less destructive off-airport landing fields, and better at managing energy to get to such a spot.

Depends on your definition of "fly". If you simply mean flying a plane-like object around in they sky, the fuel spent on a glider tow might only be 5-10 minutes worth, and on a good day you can stay up practicing your technique for hours. Your up-time-to-fuel ratio can pretty low, though I can't say the environmental impact of the manufacture of the two planes involved.

And the ultralight with hang glider wing and little Rotax or Jabiru engines are also flying, burning measly amounts of fuel. Some even have cabins.

@CrossRoads Problem in the UK is, it's usually very windy year round, making ultralights / hang gliders not an option

@Cloud - In a hang glider or paraglider, the wind is your friend, up to a point  :)

@DaveGremlin I think that point is surpassed usually here :)

@Cloud - I think the BHPA and the local clubs would disagree

By using flight simulator where possible.
Running the simulator is definitely more environment friendly than running even a small aircraft. A very high end computer with multiple CPUs and several video cards maybe would use 1500 W of power under full load (this is how much the most powerful PC power supplies are rated). Maybe multiple large monitors would use few hundreds more. This is next to nothing in comparison to 75000 W required for launching even a glider.
Of course, simulators can only replace part of the training but especially in cases when somebody has enough hours but for some reason not enough skills to pass the test, this could probably work.
This answer assumes certified simulators like this one for CESSNA 172, certified. I mean, not a PC running a star wars computer game with just mouse and keyboard attached.


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Why aren’t there any lifting-canard airliners?
A lifting-canard aircraft, such as the Long-EZ, is an aircraft with the main wing at the back end of the fuselage and a pair of small, highly-loaded canards attached to the forward fuselage; the canards fly at a higher angle of attack than the main wing, and, consequently, provide a significant amount of lift in addition to pitch control.1
During a sharp pitchup in a lifting-canard aircraft, the canards, being at a higher angle of attack than the main wing, stall first, causing the aircraft to automatically pitch down before the wing ever stalls.  As the wing, with the ailerons on it, remains unstalled throughout, roll control is preserved, without any of the violent rolling inherent in stalled control-tail aircraft.2  As the canards are stalled, pitch control is lost until they unstall, but, in this case, you don’t need pitch control, because the aircraft pitches down and recovers all on its own, without the need for any manual control inputs;3 this actually has the benefit of making lifting-canard aircraft practically unstallable (for the main wing, anyways) barring the separation of large parts of the airframe.  In addition, as the surface providing most of the aircraft’s lift never stalls, the overall loss of lift when the canards stall is fairly minor, and the aircraft’s handling characteristics remain benign throughout.
In contrast, while a control-tail aircraft will usually also pitch down when the main wings stall, this is dependent on the stabiliser trim setting, and, if the center of mass is near the forward limit (necessitating considerable nose-up stabiliser trim), the aircraft may actually pitch up in a stall.  Also, if the aircraft does pitch down, it does so quite violently, as the majority of the aircraft’s lift is suddenly lost, and with large, violent, largely-uncontrollable roll oscillations (as the ailerons are located on the main wing, which is stalled).  And, because the surfaces used for pitch control are not yet stalled, pitch control is preserved, allowing the pilots to hold the aircraft in the stall.
Given the considerable safety advantages of the lifting-canard configuration, why don’t we see any lifting-canard airliners?

1: As opposed to a control-canard aircraft, such as the Flyer, where the canards fly at a nominally-zero angle of attack, are used only for pitch control, and make these aircraft utter beasts to fly without a computer making constant control inputs.
2: Aircraft with a tail-mounted horizontal stabiliser and elevator which (nominally) fly at a lower angle of attack than the main wings.  Examples include most aircraft ever.
3: In contrast, control-canard aircraft pitch violently up as they stall (because the main wing, being at a higher angle of attack than the canards, stalls first), and, therefore, require aggressive nose-down control inputs to recover before the canards stall as well and pitch control is effectively lost; lifting-tail aircraft (with a tail-mounted horizontal stabiliser and elevator that fly at a higher angle of attack than the main wings) also pitch up, for the same reason, except that this happens well before the main wings stall, and is coupled with a simultaneous, near-total loss of pitch control as the horizontal tail stalls (making stalls completely unrecoverable for lifting-tail aircraft using only the usual aerodynamic surfaces for control).

I wish I could substantiate this, but I think people think an airliner should "look a certain way," and that influences the design. It makes me think of the "Battle of the X-Planes" documentary (https://www.youtube.com/watch?v=Y_WPLeDmU6o) where the Boeing one, looked so different than a "normal fighter jet" I think that even though the documentary made it sound like the design Boeing's plane was superior, the more "classic fighter jet looking" F22/35 design won out.  Airplanes with Canards just "look weird" to casual observers. (see also https://en.wikipedia.org/wiki/Piaggio_P.180_Avanti)

The Tu-144 was a Russian airliner that had retractable canards.

One good reason, is that airliners have main wings with flaps galore dropping down to increase the coefficient of lift at slow speeds. This also greatly increases the nose-down pitch moment, which must now be countered by the already highly loaded canard. Canard stall then becomes the limiting factor on approach speed. You either need to have a less loaded canard (there goes your natural stability) or flaps on it, or some other aerodynamic kludge.

Sean I have no idea where you got the idea that the horizontal tail on a conventional aircraft lifts up, like a canard surface but at the opposite end, and can therefore stall and let the nose rise.  It's exactly backwards.
The tail lifts down.  When the airplane stalls, the center of lift of the main wing shifts sharply aft creating a strong nose down pitching moment that the horizontal tail lacks authority to counteract until the plane speeds up, and the nose drops.  If the down lifting tail surface itself stalls, that is a disastrous situation and is abnormal for any aircraft.
Canards generally suck because they have a host of limitations that negate most of the theoretical benefits and that's why they have been commercial failures. Otherwise, you'd see lots of them.

A horizontal tail only produces downforce if the aircraft's center of mass is forward of the center of lift of the main wings. With an aft center of mass, the tail lifts up.

Which is WAAYYYY beyond the aft C of G limit, that limit being at least 5-10% of chord forward of the most forward center of lift position.  You can't load the seesaw so it wants to tip the wrong way. An airplane loaded that way will crash, like that 747 freighter taking off from Kabul with the load that shifted.  You need to do some research on how airplanes fly my friend.

I did my research before ever asking this question.  "It is sometimes assumed that on a stable aircraft this will always be a net down force, but this is untrue." "The real rule is just that the thing in back needs to fly at a lower angle of attack than the thing in front. If the angle is so much lower that it becomes negative, that is just fine, but it is not required."  You need to free yourself from the negative-lift misconception, my friend.

Wish to constructively add (737 inspired)  3 solutions to help if your H stab/elevator/trim system is does not produce enough lift to "save the 747" or "737":  1. Make it bigger. 2. Lengthen the fuse.  3. Do both.  IMHO a large rapidly moving trim is probably the the worst solution for the Max 8.  I would suggest a very slow or manual setting of Hstab trim.  A smaller trim tab for constant rapid inflight trim control (computers are good at this) that is easily overridden manually with the elevator might be safer, along with superior passive pitch stability of a larger Hstab.

And BTW, engine thrust line is also important for a slow flight "save".  Unfortunately, underslung engines with a pitch up moment added to the aft loaded 747 woes.  Not saying it could have been saved, but sound design improves the odds.

@Sean Here's a simple description of how it works http://learntoflyblog.com/2016/06/27/aircraft-performance-pitch-stability-stability-part-2/.

@RobertDiGiovanni I understand that the thrust line isn't any lower but that the thrust amount is higher, and the engines are more forward and just fatter, causing me to suspect that there is an increased pitch up moment caused by the lift being generated by the nacelles themselves at high AOA.

@John K that seems to be the prevailing thinking, and why I am harping on canards.  I pray Boeing gets this worked out and preach solid engineering fundamentals.  Building free flight models and deliberately leaving off any control surfaces, just trying to size and set the Hstab angle right, has taught me much.  Back to basics!

None other than the great Clarance Kelly Johnson had similar thoughts in the 1930s, before testing validated the advantages of rear mounted stabilizers.
The Achilles heel of canard designs was that once relative wind shifted to beneath the aircraft at high AoA, the lower surface of the canard acts as a lever to push the nose up even further.  The US Army Air Force Ascender required additional area to be added behind the CG to counter act this tendency.  Secondly, a loaded canard essentially makes the airplane a less efficient biplane.
Let's also clarify one very important basic aspect of forward set CG and downforce on tail design. As the plane loses speed, the forward CG pitches the nose DOWN.  As the plane gains speed (increasing aerodynamic forces)  the elevator trim pitches the nose UP.
Notice with a properly designed rear mounted horizontal stabilizer (also validated by around 150 million years of bird evolution) the forward wing also stalls first.  It would serve us well to review the design of the horizontal stabilizer/elevator/trim system.
Firstly, a review of tail force created at various AOA.  Yes, at lower AOA the tail creates DOWN force to balance main wing lift force and CG.  What happens at a higher AOA (even without change of trim or elevator input) ?.  The tail force of a properly designed horizontal stabilizer of ADEQUATE AREA should begin to generate UP force BEFORE the plane stalls, to compensate for the forward shift of the wing center of lift and help push the nose down.
Of course control inputs help this, excessive ones should be unnecessary.
Notice the canard design is nothing more than a tiny wing and a giant tail.  This is why deltas (lots of rear area, stall at higher AOA) go so well at the back end with canards up front, which also makes a successful supersonic design.
But in the fuel efficient high subsonic realm, planes will probably look "the same" for a while, just like birds. But it may be good to keep working on that tail.

Second last para is a problem Robert. The "giant tail" of the canard is lifting up.  One of biggest problems with canards is that to get good pitch behavior with speed changes to have good positive stick free stability,the canard wing has to have a custom airfoil with a lift slope that is steeper than the main wing so that it pitches up with speed with no control input. Rutan addressed it with the U of Glasgow airfoil, which had nasty problems with rain sensitivity. Builders had to put VGs on their canards to stop the pitch down in rain. A new airfoil was developed later that didn't need them.

The solution is where the CG is set.  If it is far enough behind the tiny "wing"  (using standard nomenclature) it will work.  The result the giant tail now can lift "up" at cruise and its huge size allows the plane the retain adequate directional stability.  The design will look a bit like the XB-70, which will do Mach 3 but cannot match the efficiency of the Dreamliner.  Yes, the tail lifts, but the canard lift curve can start at a lower AOA and stall first (straight wing canard with delta wing aft). See the Fokker Triplane! They knew slow flight.

Will look into the new canard airfoil, also the Piaggio P.180 Avanti has a canard AND a tail plane.  It's  canard may be able to get some lift out of the compressed air at the nose.

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Why was the 737 main rudder servo valve’s vulnerability to causing uncommanded reversals never discovered in testing?
As was discovered during the NTSB investigation into the crash of USAir Flight 427, the design of the servo valve inside the main rudder power control unit (PCU) formerly used on 737 Original- and Classic-series aircraft was vulnerable to causing uncommanded rudder reversals if the valve’s secondary slide jammed to the valve housing at a position sufficiently far from neutral (the precise threshold varies depending on the valve and whether the secondary slide jammed in the extend or the retract position).
The valve was designed so that a secondary-slide-to-valve-housing jam would not cause a reversal:

(Image source, page 83 of report/page 107 of PDF file)
However, if the pilot applied a sufficiently fast, abrupt rudder input, this would cause the valve’s primary slide to overtravel past the secondary slide, porting hydraulic fluid in the wrong direction and causing the rudder to move in the direction opposite from that commanded, all the way to its blowdown limit:

(Image source, page 84/108)
Given the potential catastrophic results of an unexpected rudder reversal (especially at lower airspeeds), why wasn’t the valve tested to make sure that it would, in fact, react to a jam in the manner in which it was designed to do so, and, if so, why wasn’t this failure mode discovered in testing?

After the accident the NTSB did very extensive testing on the PCU to determine the cause of the failure. In addition to the flight 427 PCU they tested new units, units that had been removed from other aircraft, and the units from three other crashes (SGR517, UAL585 and SLK185) as well as one selected by Boeing that had minimum tolerances.
They subjected the units to numerous tests. They could not get any of them to fail under any conditions expected during flight. The only test they could get a failure on involved an extreme temperature differential of injecting very hot hydraulic fluid suddenly into a very cold PCU. The report states "The extreme temperature differential produced during this test condition would not be expected during normal flight operations." (NTSB report page 79)
All of the PCUs passed the testing procedures for certification even after the failure testing. The temperatures of the PCU and hydraulic fluid on a 737 during flight were tested by Boeing and did not match those used for the testing.
So the PCU can only be made to fail under specific, fairly unrealistic conditions that would not be expected during flight. There was no evidence that those temperature conditions were even present during any of the flights where PCU failure was suspected. There was no reason for testing the part during design or certification in conditions that would not be expected to occur.

So you say that … the accidents never happened? The PCU failed on four separate occasions in the same way, so there must have been a real-world failure mechanism.

@PeterKämpf Not saying that at all. I'm saying that whatever real-world conditions caused the failure were clearly outside any parameters the manufacturers had expected to exist. They knew from the accidents that the part could jam, but had a hard time replicating it. I'm also not opining as to whether they should have thought of those specific conditions, only that they didn't.

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text:
Do fly-by-wire fighter aircraft automatically reverse the direction of control surface deflections during a tailslide?
During a tailslide (a flight regime where the relative airflow over the aircraft is from the tail towards the nose; i.e., an attack angle between 90º and 270º; i.e., the airplane is moving tail-first), the airflow over the aircraft’s control surfaces is in the opposite of the usual direction, causing deflections of the aircraft’s flight control surfaces to produce motions opposite those that would be produced in forward flight (for instance, in a tailslide, applying up elevator will cause the nose to pitch down, and left rudder will yaw the nose right).
Given that:

modern fighter aircraft use computerised fly-by-wire control systems instead of the mechanical linkages used in pre-21st-century fighters;
fighters are optimised for extreme maneuverability to the extent that a tailslide would be very easy to enter;
intentional tailslides could easily occur during combat maneuvering, or - even more likely - during an airshow;
and the control reversal inherent in a tailslide, like all types of flight control reversal, could easily kill an unwary pilot;

do modern fighters, during a tailslide, automatically reverse the commanded direction of flight control surface deflections relative to the direction that would be used in normal flight (for instance, applying down elevator rather than up if the pilot pulls back on the yoke in a tailslide)?

While the reversal of flight controls does happen, it is transient in nature, and in virtually all cases if you let the aircraft "fly" itself it will pitch down and recover.
Only aircraft with thrust to weight ratio of at least 1 to 1, and thrust vectoring of some sort if a jet, will be able to maintain the nose high attitude.
Prop aircraft are a different story as they essentially "hang" from the prop if the engine can develop enough power to do that.
Recovering from a tail slide is not like recovering from a stall or spin, you can't really use flight controls for anything until the aircraft develops enough airspeed for them to be effective, and in 100% of the times I have been in one, by that time the relative wind is normal and not reversed.
The exception is in prop aircraft where the prop wash against the rudder and elevator does provide some control effectiveness, but not reversed.

Good answer.  I will add that the pilot will never "fly" the airplane backwards in the conventional sense of the term.  Such a situation is considered a departure from controlled flight, and aircraft specific training will direct the pilot to hold controls in some (likely neutral) position until oscillations stop, and hopefully the aircraft ends up nose low with increasing forward airspeed from which a normal recovery can be made.

There is no difference between prop and jet aircraft (or aircraft with pusher props, for that matter) in this regard—since the thrust axis is constant relative to the aircraft, the position of the engine along the axis has no effect on stability. You may also note that helicopters are actually unstable in both pitch and roll.

This answer seems to be focused on an unintentional tailslide - I was more thinking of something to aid with control during an intentional tailslide (such as during an airshow or a dogfight).

@sean Only thrust vectoring will do what you are thinking of, but I may be wrong.

@JanHudec you bring up a very interesting point in that I was assuming the desired answer was only in the context of fixed wing aircraft. On helos a tailslide would be a totally different animal, no? :)

@JanHudec And actually there is a difference between props and jets. In a jet the thrust will be in the rear. In a prop aircraft it will usually be front and center, so the propwash can in fact be partially used for flight control.

@Sean And in composing my answer I was thinking of aerobatics, not unintentional tailslides. But either way, the aerodynamics is the same.

@JuanJimenez, true, the propwash does make a bit of difference. It can be replaced by thrust vectoring in jets.

@JanHudec Well, no, it can't, because the exhaust of a jet engine rarely flows over any flight controls. Propwash does. Vectoring will give some limited control, but not like flight control surfaces.

@JuanJimenez, vectoring will give some limited control exactly like flight controls with only prop wash over them. There is not that much difference between the situations.

Good luck with that. If that were the case, why have flight controls in the first place? Vectoring could replace them...

No.
Two main reasons.
First, no fighter aircraft is optimised (or even designed for) tailslides. They even lack basic sensors to measure air data (airspeed, angle of attack) in such conditions. Those that can do tailslide, do it as a stunt rather than as a useful manoeuvre. It's been speculated about a lot, esp. since Su-27 and MiG-29 became known, but all potential use cases put forward were highly theoretical. Even today, a dogfight is largely about energy management, and by performing a tailslide you expend most of your energy...
Second, if you think about it, you don't want to reverse controls. When you pull the stick/yoke, what you really want is not 'nose up' but rather 'go up' (if we start off the level flight), or more accurately, to create a positive load. In a tailslide, this means 'tail up'! Which will be served with the same elevator sense (provided there is enough 'negative' airflow, and, of course, much less efficiently). The same for rudder. The only control you may want to reverse is ailerons.
If you develop enough negative airspeed, your statically stable aircraft (in pitch) will probably become unstable and may require a different kind of control, but that's another story. Practical designs are even farther from this condition.
That said, modern FBWs may reverse controls, and they do it in less exotic situations. Perhaps the most practical example is ailerons reversal in near- and post-stall regime. In such conditions, FBW may start issuing 'opposite' commands to the ailerons, or even do something more sophisticated like driving a single aileron or coupling the roll command with rudder, all in order to provide 'conventional' controllability even after stall. If the flight control system treats tailslide as stall, you may have the reversal you asked for; but I don't know real FBW designs to such level of detail to affirm that.


text:
Can I fly a paramotor after learning on a paraglider?
This video has inspired me to spend next week doing a 6 day paragliding course. The only downside is the school near me don't teach paramotoring.
Could I buy (and safely use/self-teach) a paramotor after learning to paraglide?

Are you asking about the legality of flying a paramotor after doing this course or about how safe that would be?

It's never safe to teach oneself to fly anything. Aviation pioneers did that out of necessity, but many died or got badly hurt doing it. Training gives you the benefit of decades of hard-won experience without the underpants soiling moments and broken bones.
You are talking about going from being an inexperienced paraglider pilot to a complete novice powered paramotor pilot without the benefit of any mentoring or coaching.
It's a bad idea™

A friend of mine who was a private pilot SEL flew a Powered Parachute (the thing w/ a seat and wheels) w/ no training other than a few minutes of instruction from the owner.  He survived.

He had instruction then @quietflyer

True, also it was a bad idea in my opinion

I agree @quietflyer, a tandem lesson or two would have been a good idea!

@quietflyer, he still had a general flight training, and was probably fortunate not to encounter any of the paraglider-specific issues like collapse. Most of the training, for any flying machine, is about how to handle various failures, and paragliders have their specific failure modes.

No. There is a reason it is strongly recommended to do a conversion course.
As a paraglider pilot your skillset is focussed on very different aspects to the most important skills for paramotoring. You may be good at ridge soaring or thermally or XC or strong wind launches for coastal flying. Almost none of these skills are relevant to most paramotor aviation.
The following is an example of some of the things you should learn before flying paramotors that you will not have covered before as a freeflight paraglider:

Safety - both in terms of prop safety, both on the ground and in the air as well as pre-flight checks, maintenance, fuel/fire safety, ear defenders, ground starting.
Theory of flight - things like reflex profiles, trimmers, hang points, torque, how throttle power affects pitch/angle of attack, etc.
Motor - in addition to maintenance and safety issues, things like storage and transport, breaking engines in, oil ratios, fuel types, assembly, repair, types and sizes of prop.
Launch/landing - powered launches are very different and you'll have to learn to taxi, to ground handle with a heavy engine on your back, a completely different body position for launching, again torque effects while taxiing, how best to abort launches, how to avoid burning your wing on a hot exhaust or getting lines caught in an idling prop.
Airspace, navigation and comms become a much larger facts in powered flights.

And of course many other aspects.

Of course you can. In terms of flying skills, assuming you’re a good paraglider pilot you already have the prerequisite skill to fly paramotor. The only thing you’re missing is ground school in air law and weather. And in some countries (not the US) you are required to have license and registration. Sounds funny but is true.


text:
What aircraft model is this that crashed?
Could someone please tell me what aircraft type this is? The crash happened very near to my flight school a few days ago and I want to know if it was one of their fleet that crashed.

This is why it's generally a bad idea to head for roads during forced landings unless there are no other options, say because of rocky/hilly terrain. And if you do, look for poles/towers, not wires, when trying to make it down.

This question shows zero research effort. It's not hard to type the clearly visible registration number in any search engine.

If you want to know if one of your flight school's aircraft crashed, why not ask the flight school?

@Sean That's rather insensitive. "Hi, I'm just calling to see if one of your students died today..."

That was a Cirrus SR22T, registered in Guernsey as 2-RORO.
The registrar published a statement including the following information:

The Guernsey Director of Civil Aviation (DCA) and SGI Guernsey Ltd.
  (2-REG) confirm that an accident involving a Cirrus SR22T aircraft,
  registration 2-RORO, occurred on May 12, 2019 between Raglan and
  Abergavenny, Monmouthshire, Wales, United Kingdom. The accident
  aircraft had been registered in Guernsey since August 1, 2018. The
  three occupants of the aircraft were reportedly taken to hospital with
  minor injuries. No further casualties have been reported.

According to the Aviation Safety Network, 2-RORO was owned by Transport Safety Resolutions Ltd. On May 12th, 2019 it departed from Denham (EGLD) and crashed at the A40 in Monmouthshire, Wales, UK:

The aircraft hit some overhead trainwiring during a forced landing and
  impacting a main road between Raglan and Abergavenny, Monmouthshire,
  Wales. It was consumed by the post-impact fire.

Image of better times by Andrew Goldsmith on Flickr, 09-05-2019

There was already an (only seemingly similar) event on the A40 between Raglan and Abergavenny in June 25th, 2016. A Piper PA-28 (G-SVEA) tried to depart from Abergavenny airfield - a gras strip just next to the A40. It stroke some trees, veered onto the highway and crashed into the central lane separation.

Maybe it's the broken wing, but the registration could also be 2-RORG. I must admit, my initial instinct was 2-RORO, though.

Other than paint, I'm not seeing the resemblance. Must have been one heck of a crash.

Even with the last letter being a little difficult to read, plugging 2-RORG into a search engine comes back with no useful results for me, while 2-RORO gives plenty of aviation-related hits.

The information published by 2-REG is authoritative. I changed the text to put more emphasize on the link.

Exactly, it wasn't clear and I wanted more info on the incident. Not sure why the downvotes, please upvote, thanks.

This is a Cirrus SR22T owned by Transport Safety Resolutions Ltd according to this list of the 2-REG Aircraft Registry.

Correction - it was a Cirrus SR22T.  Now it's a heap of scrap metal.


text:
Are pilot YouTubers breaking any rules?
Recently, I've been watching a few YouTubers (mostly FOs) who make great videos like this:

Then I realized... They must spend a lot of time setting up cameras, playing with them, hitting record and stop etc. This could potentially distract them or make them miss something (a warning, a pre flight check etc)..
Are they breaking any formal rules doing this? If an accident occurred during filming would they be under investigation due to negligence?

If the FAA considered making videos itself (i.e. separate from any unrelated rule violations within those videos) to be a problem, they would have put a stop to it long ago, either by explicit rulemaking or the catch-all "careless or reckless" when no other rule applies. They haven't, at least with respect to GA pilots--who are allowed to do all sorts or things that charter and airline pilots are not.
Several YouTubers I follow have said they mount the cameras and start recording before preflight, don't touch them again until after the plane is down and secured, and edit out the boring parts later that show this.  That seems to mitigate the physical safety issues.
The other issue is pilot distraction if they're talking to the camera, but I don't see that as any worse than talking to passengers, which is commonly accepted within reason, and is perhaps less of a risk since the camera doesn't talk back.

Note that talking to someone next to you is less distracting than talking to someone via a cellphone (article). The fact that the camera doesn't talk back is a point in its favor, but it may not be obviously less risky than talking to a passenger.

You can get into trouble for your videos. Stevo1Kinevo had to remove all of his videos that were taken on Part 135 trips and had to take a 709 ride. I gather that it wasn’t due to distraction so much as rules related to Part 135. He was also dinged for not using checklists, but he had the raw videos that showed that he does use them.
I suppose you could be charged under §91.13   Careless or reckless operation. if you video yourself doing something careless and/or reckless.

What sort of rules related to 14CFR135, if I may ask?

@Sean He never said. I suppose it had something to do with the Operating Specifications that the charter was bound by, but I have no idea.

@Sean I read/heard somewhere that the FAA said he was breaking the rules on sterile cockpit operations (135.100) by providing running commentary in critical phases of flight during part 135 operations ("engaging in nonessential conversations within the cockpit"). I assume that means most of his videos are now made during part 91 flights, like repositioning. I don't have any source, but it seems plausible at least.

Outside of a departure or arrival, with the autopilot engaged, and one pilot monitoring, the other pilot can do headstands, play a game on his tablet, read, take a snooze, fill out log books, go for a dump, or... use a video camera.  It's not a big deal.  I've shot video to pass the time during cruise.
The general rule (as in good airmanship) is no screwing around during a higher workload phase like departure or arrival and especially below 10000 ft (including superfluous talking... non-flying chit chat should stop below 10000 ft).  During those higher work load phases, if a camera is set up to record, it needs to be set up in a way that doesn't require any attention or cause a distraction.

The FAA does have specific regulations that could apply to making videos during part 135 and part 121 flights. As JScarry explained in his answer the part 135 rules may have been used against one prominent Youtuber.
135.100 says (emphasis mine):

§135.100   Flight crewmember duties.
(a) No certificate holder shall require, nor may any flight crewmember
  perform, any duties during a critical phase of flight except those
  duties required for the safe operation of the aircraft. Duties such as
  company required calls made for such nonsafety related purposes as
  ordering galley supplies and confirming passenger connections,
  announcements made to passengers promoting the air carrier or
  pointing out sights of interest, and filling out company payroll and related records are not required for the safe operation of the
  aircraft.
(b) No flight crewmember may engage in, nor may any pilot in command
  permit, any activity during a critical phase of flight which could
  distract any flight crewmember from the performance of his or her
  duties or which could interfere in any way with the proper conduct of
  those duties. Activities such as eating meals, engaging in
  nonessential conversations within the cockpit and nonessential
  communications between the cabin and cockpit crews, and reading
  publications not related to the proper conduct of the flight are not
  required for the safe operation of the aircraft.
(c) For the purposes of this section, critical phases of flight
  includes all ground operations involving taxi, takeoff and landing,
  and all other flight operations conducted below 10,000 feet, except
  cruise flight.

For part 121, 121.542 says essentially the same thing, with an additional section banning the use of electronic devices at duty stations for non-flight purposes.
I remember reading or hearing somewhere (maybe reddit) that the FAA went after Steveo1kinevo because he was making videos during part 135 flights that included a lot of commentary during takeoff and landing, i.e. "nonessential conversations" during critical phases of flight.
In any case, clearly recording videos during takeoff and landing in 135/121 flights is no problem; there are hundreds of them on Youtube and airlines even use them in promotional materials. It seems very likely that the FAA's real concern is distraction, i.e. not just recording but actively participating in the video.


text:
Are there any 100% renewable energy aircraft in development?
There seem to be several options for aircraft R&D regarding cleaner fuels for the time when fossil fuels are no longer economically viable.
Some of these include:

Algae. A drop-in fuel. These fuels are being used and developed in co-operation with the USAF. They have had several successful test flights.
Batteries. Doesn't seem viable at this stage.
Nuclear reactor on board. Doesn't sound safe.
Hydrogen. This wiki page says they could be built by 2020. That's only a year away now...

I've found a few examples of test prototypes & flights using fuel mixtures that improve emissions and gasoline consumption, but are there any commercial aircraft in development, with an expected launch date that utilize 100% renewable energy?

Please do not confuse energy sources with energy storage. Rechargeable batteries and hydrogen are storing energy. Charging batteries or producing hydrogen with electric power that is generated from fossil fuels to replace fossil fuel is counterproductive.

https://zunum.aero

I wouldn't call a nuclear reactor a renewable energy source...

@Bianfable: Certainly a nuclear reactor can be renewable.  See "breeder reactor" for details.  Now hydrogen, OTOH, is (in current implementations) about as far from renewable as you can get.

@bogl Besides, how were the batteries produced? Not a particularly renewable process either.

Not commercial, but I'm surprised no one's mentioned the Solar Impulse in the comments yet. It's 100% solar, has circumnavigated the world, and ...sounds pretty miserable to fly.
https://www.theguardian.com/environment/gallery/2016/jun/23/solar-impulse-2s-flight-around-the-world-in-pictures

Contrary to one clause of your question, there are a number of battery-electric light aircraft (or what the USA calls "light sport" class) in development, with prototypes flying.  This includes both fixed-wing conventional types with single or multiple electric powered propellers, and "drone" style craft using what amounts to thrust hover with electric powered propellers.  Flight time is limited, but better with the fixed wing types -- enough so that I'd call an electric motor glider a very feasible design.
Hydrogen has limited usefulness, for the same reasons it doesn't work well for cars: it's technologically difficult to store enough for reasonable range.  Either extreme pressure, extreme cold, or a chemical storage method that limits the rate at which you can draw fuel are reqired.
A submarine type nuclear reactor was operated aboard a modified B36 in the 1950s -- the project, intended to lead to a strategic bomber with a flight time of weeks or months, was dropped due to lack of need as well as cost and safety concerns (most of the safety concerns, such as "roll-up" explosions, were later resolved or found to be overblown).  This kind of power isn't "fully renewable" anyway -- fission fuel must be mined, it isn't grown.
Algae fuels, as drop-in replacements for kerosene, may have some usefulness, but there are storage issues (hard to stockpile something that can mold or rot) -- as you note, however, testing is in progress, and we'll know in a few years.

Comments are not for extended discussion; this conversation has been moved to chat.

Algae fuel is basicly vegetable oil, could be mixed with diesel for storage.

Yes, there are projects to power the jet engines by oil from plants: canola (rapeseed), coconuts and soybeans. This fuel is also cleaner (less sulfur) and even freezing point (-47 degrees C) is acceptable.
While not an immediate certified replacement, these oils can work as jet fuel without radically re-designing the engine. Some refining technology and suitable engines are under development.
Planes with piston diesel engines could also probably run on this fuel.

Batteries are indeed more feasible then you give them credit for. For short hop flights they are actually within reason:
https://arstechnica.com/tech-policy/2018/10/scotlands-orkney-islands-may-see-electric-plane-service-by-2021/

...the added benefit of electrifying the Orkney Islands flights is that there's an abundance of renewable energy, especially wind energy, already on the grid in the area.
Though replacing the jet fuel burned by small island-hopping planes in a remote part of the world may seem like a drop in the bucket in efforts to reduce emissions, starting small is often a path to thinking big. If the shortest flights in the world can be flown successfully, gradually longer and longer commercial electric flights may someday be attempted.

Norway is also setting a goal of entirely electric-powered short-haul flights by 2040: http://www.bbc.com/future/story/20180814-norways-plan-for-a-fleet-of-electric-planes

You might also add a BBC article on Norway - http://www.bbc.com/future/story/20180814-norways-plan-for-a-fleet-of-electric-planes


text:
What has Airbus done to address the dual input issue?
There have been a couple of fatal incidents involving Airbus aircraft, namely Indonesia AirAsia Flight 8501 and Air France Flight 447, that could have been prevented had the captains orders / input been the only accepted one. In both cases the captain was commanding push down to recover from a stall, while the FO was pulling up. Because of the dual-input system they cancelled each-other out and the stalls were not recovered from.
Has Airbus done anything to address this? It seems to me that if the aircraft is in alternate law, as it was in both cases, perhaps it should only accept input from the left seat.

You mean besides each side's priority switch, never mind CRM? For what it's worth, there have been many accidents where the captain has been in the wrong, too, so clearly "blindly trust the captain's input" wouldn't be the correct approach either. See Who has the final authority over sidesticks? and Why is the Priority Takeover button used? and probably some others.

@MichaelKjörling It was just an example. I don't know about the priority switch.

"Only accept input form the left seat" is a very bad idea. What if the reason the airplane is in alternate law is an accident that not only damaged the airplane systems but also knocked the captain unconscious? Also, the assumption that the captain is also the pilot flying is on thin ice. Yes, in case of unforeseen circumstances, often the most experienced pilot will take the controls, but … who is to say that the captain is actually the most experienced pilot for this particular type of aircraft in these particular circumstances? Also, what if flying the aircraft isn't actually the most …

… demanding task at the moment, but rather figuring out what the hell happened? In that case, you want the most experienced person (which might be the captain) to work on figuring out the problem, and "the other guy" flying the plane. What if the left seat is unusable as a result of the accident?

Adding to @JörgWMittag's comments above, consider British Airways Flight 5390 in June 1990. If that airplane had had control stick input addition similar to that of FBW Airbuses, the copilot could just have pulled his stick full aft while the captain was wedged against the left side controls to maintain a roughly neutral pitch. Instead of a critical, unanticipated descent, it might have been more like the trim being stuck at a nose down attitude setting, even without priority override.

@MichaelKjörling Big difference is that flight didn't involve any fatalities, the two that I referenced did

Both mentioned accidents happened because neither pilot maintained anything resembling situational awareness. It had nothing to do with the control system; struggling over connected control columns is unlikely to have been any better.

re: "In both cases the captain was commanding push down to recover from a stall": In the case of AF447 the captain was NOT at the controls during the accident sequence. He was not even in the cockpit at first and had to be called into the cockpit urgently. He then took place behind the two First Officers and remained there until impact.

@summerrain Yes AT WHICH POINT he commanded push down but it was too late with only 2000ft to go....

I would suggest Armavia Flight 967 was a similar accident where both pilot side stick input was an issue in the last moments.

It's not clear that there is an issue.
Is the lack of coupling actually a lack?
The lack of coupling between the two side-sticks to provide feedback between the pilots is, intuitively, a lack in the interface.
We are used, in the physical world, to being able to feel what another person is doing through the things that we're manipulating, the machinery and tools we operate together.
However, flying a plane is not like carrying a ladder up a narrow staircase, or riding with someone on a tandem bike. That kind of implicit bodily feedback isn't part of the Airbus cockpit system.
Cockpit communication is supposed to be explicit
Instead, the communication is supposed to be explicit, so the pilots say what they are doing when operating the controls. Introducing physical feedback into that environment might seem like an enhancement, but in fact it would be the opposite: it would be the introduction of a source of doubt, that draws habit and practice away from the explicit communication around which the system has been designed, towards an implicit form of communication.
Even implicit communication requires verbal confirmation
It would then be necessary to introduce also a new system under which the pilots would decide whether their explicit verbal communication is now in operation ("I have the controls"), or the implicit physical communication (you feel the other pilot doing something).
Now there is a new burden! As well as deciding what they should be doing with the controls, the pilots must also decide whether they will be prioritising explicit/verbal or implicit/physical communications - two things to manage.
And working that out will require explicit verbal communication, so they may have well just stuck with that in the first place.
And if implicit physical communication is allowed to have weight, they still need explicit verbal confirmation of it, because that's what pilots always do. By the time I have asked my co-pilot "WTF are you doing with the stick and why?" it's already later and more stressful than if they had said in the first place that they were taking the controls to climb over an unexpected mountain.
It's not a lack, it's the removal of something unwanted
Implicit communication through the side-stick is not a free gift of additional useful communication. In the Airbus cockpit system, it's the introduction of something dangerous and unnecessary, that would require extra cockpit management and would harm communication in the cockpit.


text:
Why were there so few general-aviation aircraft in South Korea in the late 1990s?
While reading the AAIB report on the crash of KAL 8509, I came across (in section 1.17.11, “Korean aviation statistics”) this surprising information regarding the South Korean aircraft population in 1997:

[...]  In addition there were 57 aircraft (including helicopters) operating in the commuter and non-schedule area of the market and 44 general aviation aircraft.  [...]

(Page 58 of the paper report; page 70 of the PDF file of the report; emphasis added.)
This is a mind-bogglingly tiny number of general-aviation aircraft for a country with as many people as South Korea (45.95 million in 1997), coming out to less than one general-aviation aircraft per million citizens; in contrast, in the same year, the U.S. had slightly under 200,000 general-aviation aircraft distributed among 272.9 million citizens, or approximately one general-aviation aircraft per 1,200-1,500 citizens.
Why was the South Korean population of general-aviation aircraft so small in the late 1990s?

Considering that just over 50% of the world's GA aircraft are in the US perhaps you should be asking why the US has so many, rather than why South Korea has so few? :-)

Consider that South Korea is a small country - at 38,691 mi^2, it's smaller than all but 13 US states - and geographically isolated, so there aren't really all that many places to fly to within the country.  Outside, about the only place within practical GA range that's also politically accessible is Japan.  It was also quite poor until relatively recently.


text:
Why are the 737's rear doors unusable in a water landing?
The 737's rear exit doors cannot be used to evacuate the aircraft in the event of a water landing, as shown, for example, in this safety card:

(Image from flight-report, via Jordy here at AvSE.)
In contrast, the rear doors on (for instance) the A320 series can be used for a water evacuation:

(Image by Czechnology here at AvSE.)
Why can't the 737's rear doors be used during a water landing?

I like the optimism of these "safety cards" showing a pristine aircraft floating nicely on the water after a ditching. Statistically unlikely but makes for a pleasant looking card.

There was that time a guy with a lot of glider experience landed an airliner in the Hudson River a few years back, after the engines died right after he took off from the airport.

Yeah, and they couldn't use the rear doors.  Know why?  They were underwater... This was an A320.

@nick012000 and they call it "The Miracle on the Hudson" for a reason.

Looks like Airbus tell you to check, but Boeing reckon it's not even worth checking. In the one photo I can find of a successful Airbus landing on water, you wouldn't open the rear doors anyway...  https://home.bt.com/images/passenger-plane-landed-in-hudson-river-136395463010202601-150114153840.jpg

The bottom of the door opening sits too close to, or below, the water line when the airplane is floating.

Comments are not for extended discussion; this conversation has been moved to chat.

It all goes back to how the aircraft is designed; the ways different planes float vary.
when the 737 ditches on water the tail-section of the plane is deeper in the water than front of it, because the wings are a huge floating point and support most of the weight of the aircraft when afloat, and the bigger front of the airplane contains more air so when floating it will be lighter hence pitching the nose up, causing the tail and the rear doors to be below or very close to the water. this is why these doors remain shut in the event of evacuating after an emergency water landing so that water doesn't get in any faster, giving the plane and its passengers and the crew more time to evacuate and stay afloat longer until help arrives.

"[T]he bigger front of the airplane contains more air so when floating it will be lighter" and, by the same argument, a big empty box weighs less than a small empty box because it contains more air! You've forgotten that the bigger container also has bigger walls, which weigh more.

@DavidRicherby You're forgetting the square-cube law.

@DavidRicherby when comes to objects with the same shape bigger objects have bigger volume to surface area ratio. So the bigger object has more trapped air to mass ratio causing it to be lighter when floating.

@DavidRicherby - Yes, bigger empty boxes weight less than smaller empty boxes when both are submerged in water.

@Pere That's not what weight means.

@DavidRicherby You are the one introducing the interpretation of "lighter" in the answer as meaning less weight rather than more buoyancy. The answer did not say the former, and clearly meant the latter. If you really want to nitpick, it is the wording, not the concept.

@Backgammon I'm not introducing anything. "Less weight" is the meaning of the word "lighter".

@DavidRicherby, the tail is a pointy cone with a bunch of thin bits of metal sticking off of it.  It's got a lot of metal and only a little air.  The nose is a rounded object containing a whole lot of air and only a little metal.  It's not surprising that the nose floats higher than the tail.

@DavidRicherby A larger empty box of the same strength has "more mass" everywhere and "less weight" when in the water. By your words, a larger empty box is "lighter" in the water. The answer specifies "when floating".

@Backgammon No. Weight is the gravitational force on an object due to its mass. Weight does not change if you're floating on water.

I see what the contention is now. Is "apparent weight in water" satisfactory? It should not be necessary to specify this in every single discussion to avoid drawing corrections when everyone understands what the shorthand means.


text:
Why was the VC10 unusually prone to reverser-induced buffeting?
According to Wikipedia, the original (“Standard”) version of the Vickers VC10 had thrust reversers only on the outboard engines, as putting reversers on the inboard engines produced severe tailplane buffeting and attendant fatigue problems.  The larger, heavier Super VC10 had modified and repositioned engine pods in order to resolve this issue, allowing the Super to have reversers on all four engines; despite these changes, the buffeting from the inboard reversers proved to still be severe enough to necessitate their near-immediate removal.
In contrast, the vast majority of jetliners with tail-mounted engines (leaving aside oddities like the F28, which has no thrust reversers at all, and the Il-62, which has four engines, with reversers only on the outboard pair, like the VC10) experience(d) little or no trouble with reverser-induced buffet, even though their engines - like the VC10’s inboard pair - are (or were) located immediately adjacent to the empennage, and, thus, should be just as prone to inducing buffet as the inboards on the VC10.  1-11, DC-9, 727, Tu-154, F100, CRJ900 - all have (or had) tail-mounted engines with thrust reversers, but none experienced the buffeting problems seen with the VC10’s inboard engines.  Why is this?

I don't think the root cause was ever fully defined. It appears this was one of those "If it hurts, don't do it" situations where they found the buffeting stopped when the inboard engines did not reverse, and they decided finding the workaround was cheaper than working out the full aerodynamic cause and fix.

Travelling on RAF Transport Command VC10 coming over the N coast of France, the Captain announced 'we're high and fast for landing at Lyneham, so we will reverse the engines, you will feel some buffeting as the rear edge of the wings stall.' So, we did that, sense of braking and shaking and we came into Lyneham for a perfect landing.
Watching 747 pilot on You Tube, he says, no plane reverses its engines until it is on the ground. Evidently not true!

It may just be that other airframes mount their engines with sufficient clearance to avoid the buffeting issues that were seen on the early VC-10's. Ultimately it only took of a move of 11 inches to solve the issue

...testing was prolonged by the need to move each engine pair 11 in (27
  cm) outboard. This major redesign was needed to resolve tail-plane
  buffeting and fatigue issues due to thrust reverser operation. The two
  inboard engines could have thrust reversers installed at last,
  matching the 707.

So while it may appear in photos that other aircraft have similarly mounted engines you would need to look at actual technical drawings to truly compare mounting distances.
Its also worth noting that there is nothing saying other aircraft do not also see buffeting from their aft mounted thrust reversers, however they may not see enough to cause structural issues as was the case with the VC-10.

Except that, even with the relocated engines, they still ended up with enough buffeting that they had to remove the inboard reversers almost immediately.


text:
Would it be a viable option to make the engine generate lift?
I was thinking that if you made the engines generate lift it might help a tiny bit with the amount of time to takeoff, and thus lowering runway lengths.

if you mean helicopters, they are already invented ;-)

For the complexity it will need to help more than "a tiny bit". There are also safety issues... what happens if there's an engine failure? Can the plane still climb safely?

that's called "short tale off", as in STOVL. google that if you don't know what that means

short answer is that wings are really good at generating lift.  Look up "lift to drag ratio".  It can be 10 - 20.  Which means for every 1 pound of thrust generated by the engine, you get 10 - 20 pounds of lift.  So you let the wings do what they are good at (generating lift) and you let the engines do what they are good at (generating thrust).  That is the most efficient design.

Good thought, and it does happen. Tilt the jet exhaust or propeller downwards at a shallow angle $\phi$, and there is lift created at sin $\phi$ while thrust is reduced by cos $\phi$. If we take small angles, let's say 3 degrees:

$\Delta L$ = T $\cdot$ sin(3°) = 0.052 T
$\Delta T$ = T $\cdot$ cos(3°) = 0.9986 T

So 5.2% of engine thrust is converted into lift, for a loss of 0.14% of horizontal thrust. Free lift! Slight angles like this are found in aircraft installations, for instance in tail mounted jet engines which are angled horizontally to reduce yawing angle with a failed engine.
With engines mounted underneath the wing,the downwards pointed thrust would help a tiny bit in lift and reduce the take-off length. As @mins points out, with tail mounted engines the nose down pitching moment may counteract the lift benefits.

That happens too, and quite clearly, in present-day, light pusher autogyros, where, in slow flight, the angle between the horizontal and the propeller axis can reach 20º and sometimes even more...

Ah yes and then the propeller helps with the CG management.

You haven't told whether this vertical lift at the tail has an impact on required takeoff length and takeoff time. It seems this vertical lift is acting against elevators during takeoff, and maybe the takeoff is longer.

@mins The moment arm of the horizontal tail is longer, net thrust is still up :)

Well, it's not "free" lift, because 1) pushing tail up and nose down generates trim drag, and 2) thrust lost to forward propulsion needs to be multiplied by the L/D ratio to see how much lift could be gained if the thrust were used for forward propulsion.

Re "Slight angles like this are found in aircraft installations, for instance in tail mounted jet engines which are angled horizontally to reduce yawing angle with a failed engine."-- wow-- is this really true?  Perhaps there's a new question in the making here.  The yawing moment (and thus torque) with a failed engine seems rather trivial in the rear-engine context compared to the wing-engine context.

@quietflyer The trim drag in cruise will be accounted for in the design process. Yawing moments with a failed engine dimensions the vertical tail, which is indeed smaller with tail mounted engines, one of the advantages. Point the thrust vector through the CoG, and the yawing moment becomes zero.

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text:
If engines are closer to the wing (or in the wing) does it increase efficiency
If you were to make an engine in the wing or at least closer to it in commercial airliners such as the 747, 737 and A380 etc. Would it increase efficiency?

Yes, mounting jet engines in the wing root increases aerodynamic efficiency due to:

No drag from engine pods
Smaller yawing moment upon engine fail, and resulting smaller vertical tail.

But that is about it. There is a host of disadvantages to mounting the engines in the wing root, one of them being that high lift devices cannot be used and the wing is bigger, causing more drag.
Three huge advantages of mounting the engines in pods, underneath the wing, in front of the aeroelasitc axes are:

High bypass engines can be mounted, vastly improving fuel efficiency.
The engines are within easy reach for maintenance.
The weight of the engines provides both bending relief, and reduces structural weight to prevent flutter.

Also see this question.

Why do some commercial airplanes not implement it? Like the b2.

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text:
How has CAD influenced aircraft design in the last few decades?
I know that computer aided design was used extensively when designing the Boeing 777, are there any other good examples of aircraft where CAD was essential in the design process?
Are there any major leaps forward in aircraft technology that would have been impossible without CAD?

This seems to be an extremely broad question. You might get better answers if you focus your question on something more precise.

"aircraft technology that would have been impossible without CAD", it depends on how you think of "impossible". Impossible is also (if not mostly) a matter of budget and time. Engineer wouldn't have been able to design aircraft that are possible to manufacture, maintain, and sell without the help of systems like Catia. It's not limited to the aircraft industry.

There is nothing being done with CAD today in aircraft design that cannot be done without CAD, as long as you have unlimited time and resources. :)

Are you referring specifically to CAD (drawing), or CAE (finite element analysis, computational fluid dynamics, etc)?

We used CATIA extensively in the design of the F-22.  It helped all the supporting "ilities" also in their tasks.  Great tool.

Thanks for the answer! Can you tell us a bit more detail about this -- what do you mean about all the supporting (lia?)"ilities"? Also, I know that Catia is a FEA force analysis tool, but I don't know that much about the process of incorporating it (and a CFD simulation) into a real design team's workflow -- how do you get forces into it from CFD, for example?

CATIA, for us was a design tool. Supportablity, reliability, quality, etc.  We did the whole F-22 program with CATiA at GA, WA and TX.  That allowed the three separate sites to have things coordinated.  We also used Integrated Product Teams (IPTs) that had their designers and own stress support, weight, producibility, reliability, CFD, manufacturing, procurement, etc.  Their were IPTs for the armament, fuselage structure, electronics, electrical installation, ECS, cockpit, transparency, landing gear, wings, empennage, ejection seat, integrated avionic racks, fuel system, hydraulics, etc., etc.


text:
What could the fuel pump failure have been that my flight experienced?
I was on an Easyjet flight (I think an A320), when mid-flight, I overheard a member of cabin crew tell another passenger there was a 'technical' issue with the aircraft, that might make us slightly behind schedule.
Naturally, I imposed on their conversation to basically ask her to repeat the issue to me in detail. She said that the 'mechanism' that transfers fuel between the two tanks had failed, and so only one tank was available.
Obviously, the flight completed without any noticeable events, but could someone explain to me what happened as I do not understand.

I don't think it's possible to answer this question accurately, since the crew member's description is so vague. You may get some good theories, but I don't know if there's any way to confirm them.

I think you may search for fuel management in A320, and possibly for procedure specific to fuel  transfer and cross feed failure. If so, please specify your question and indicate your current state of research and understanding so that we can answer as accurately as possible.

Adding flight number and date would be of assistance in case there happened to be anything reportable.

For what it's worth, you're definitely correct that your easyJet flight was on an A320 variant, as that is the only type in easyJet's fleet.

@ManuH If the asker knew about fuel transfer and cross-feed pumps, they wouldn't need to ask their question! Yes, we like people to research their questions before posting, but we can't expect them to do that when it requires much more technical knowledge than they have.

The conversation may have been about fuel pumps or fuel transfer valves but the flight attendant was probably told that as a simple explanation - it would not have been the real cause.
Aircraft have multiple systems to pump fuel, transfer, and pipe it so no single failure will affect normal operation.
For example, pumps have automatic bypass valves so that other pumps will continue the normal flow past the failed pump. No single transfer valve obstructs fuel flow. There are multiple paths to get the fuel to the engines; either directly or by transferring through a completely different set of pipes to another tank then on to the engines.
What likely happened was there was one or more FILTERS that became obstructed. Both ice particles and algae often obstruct filters. But once again all the filters have automatic emergency bypass valves and pipes. However, it is not unheard of for polluted jet fuel containing large amounts of algae to overwhelm the filters.
[ In my 10 years with Continental Airlines, we had one aircraft engine obstructed by ice particles, but numerous occurrences of algae contamination. ]

If the filters and/or bypasses either obstructed engine filters, made
  one or more tanks unusable, or reduced the fuel flow, the Captain
  would have chosen an altitude and speed that gave best fuel economy;
  and would have arrived late.

It is worth noting that algae contamination is quite severe in some parts of the world such as Asia and Pacific Island nations. It is common practice for American airliners to carry more fuel than necessary when headed abroad to help "dilute" the bad fuel in other parts of the world.

Simplified Airbus diagram of a typical fuel system showing multiple pumps, transfer valves, and paths to each engine.

B737 diagram (one of the simplest airliners) showing multiple pumps, transfer valves, and paths to each engine.

The CRJs have a gravity transfer facility built into the plumbing, pretty much an interconnecting pipe with a valve, as a back up to the normal powered transfer system.

Interesting that both diagrams seem to contradict your statement that "no single transfer valve obstructs fuel flow". The cross-feed valve in both diagrams seems to be a single point of failure between the left & right sides in both cases. Of course, you do label them as "simplified" diagrams, so there could be multiple paths and they've been simplified to a single line.

@FreeMan, the cross-feed valve is only needed if something else has already failed.  In normal operations, it's closed.

@FreeMan Also, from the diagrams it looks like it might be possible to bypass it through the center tank.

@ymb1 Thanks for clarifying that to me.

All of the §25 certified transport category aircraft I fly have fuel transfer systems that could be rendered inoperative by a single failure of one of several components or systems. The same is true for other aspects of the fuel systems, such as the high pressure fuel pumps. Your answer appears to be overly simplistic: I suggest you narrow the scope of your claims, if accurate in any specific cases, or correct the inaccuracies otherwise.

The usage and movement of fuel changes the aircraft's center of mass. A lot of aircraft have fuel pumps that move fuel between the two tanks in the wings to make sure one side does not get heavier than the other due to unequal usage of fuel by the engines and thereby, helps in balancing the aircraft while in flight. It makes the pilot's job a lot easier.

So in this case (it sounds like that is what happened), why did the aircraft not heavily lean to one side?

Usually the engines (being the same model) consume fuel at more or less the same rate, negating the need to balance out the aircraft. From what I know, the pumps are more useful when there is a significant difference in the amount of fuel in each of the tanks. However,the pumps aren't used if there is a leak in one of the wing tanks since it would just exacerbate the loss of fuel, turning the aircraft into a glider.

@Cloud the ailerons would be "off center" so that the heavier wing produced more lift than the lighter one. If nothing was done to keep the aircraft level, it would naturally tend to fly in a circle - the opposite cause-and-effect to intentionally banking the wings to make a turn. For a large aircraft the autopilot would handle this automatically. For a small plane the pilot can manually "trim" the controls, to avoid having to hold the stick off-center continuously.

@Cloud, a weight imbalance can be counteracted with aerodynamic forces (aileron, rudder, or elevator), but doing so increases drag, slowing the airplane down a bit (or increasing fuel consumption).

If there really was only one tank of fuel available on an aircraft that typically has two tanks filled, that would at a minimum mean that the airplane would have to fly on half the fuel that was intended to be available for the rest of the flight.
If such a failure happened mid-flight, as in your claim in the question, it'd mean the pilots suddenly had only 25% (of what they took off with) usable fuel, when they intended to have 50% at that point in the flight, having taken off with 100% and expecting to land at near empty. In such a case, unless you were very near the destination anyway (in which case delay would be insignificant, so no real need to tell anyone in the cabin), to not divert to the nearest suitable landing site would be irresponsible on the part of the pilots.
Since you say that the flight completed without any noticable events, it stands to reason that the flight indeed did not divert.
The only reasonable exception to the decision to not divert after half the remaining fuel becomes inaccessible mid-flight would be if the pilots took off with at least 1.5 times the fuel they needed for the flight.
Let's say that the flight required 100,000 kg of fuel, plus applicable reserves. Normally, half-way through the flight the aircraft would be down to half that, or 50,000 kg plus reserves, distributed evenly between the tanks. Assuming two tanks, that's 25,000 kg plus half a reserve, per tank. If only one tank is available, but 50,000 kg plus reserves is available, there must then be no less than 100,000 kg on board (50,000 kg of which now unusable) after burning through the fuel needed for the first half of the trip (corresponding to 50,000 kg of fuel). Therefore, the aircraft would have had to take off with 150,000 kg of fuel plus reserves, 1.5x of the required 100,000 kg plus reserves, to still be able to make it to the intended destination with the same amount of fuel remaining as intended if half the remaining fuel becomes unusable at the mid-point of the flight. Since hauling fuel around itself requires fuel (because the aircraft is heavier), pilots don't load up amounts of fuel above and beyond what they need, without very good reason. Assuming that the aircraft was topped off with an appropriate amount of fuel before take-off, the pilots would suddenly be faced with having at most half the remaining range intended; likely less, because you don't run the tank all the way down to empty, especially when the other wing is weighed down by at least 50,000 kg of fuel.
Therefore, I conclude that there must have been something going on beyond what you describe in your question.
There may have been an issue, and it may have had something to do with the amount of fuel available to the engines, but it seems highly unlikely to have been the sudden inability to use half of the fuel remaining onboard.

Thanks Michael, I wish I'd just asked the pilot after the flight now :/


text:
How safe are extreme aerobatic flights?
Statistically, how safe are extreme aerobatics flights like this one?

The maneuvers listed are not really extreme, and it is certain that, catering for the general public, they will be accomplished at a relatively high altitude. The airplane is widely used in the aerobatic field and is generally regarded as reliable. Therefore I believe that there is no more danger than there would be if you were doing a regular flying lesson.
Edit: I have dug up some more numbers for the aircraft type. There has been one non-fatal accident listed involving an Extra 300 in the Aviation-Safety database for the year 2020. From 1992 until present there have been 82 accidents listed of which 42 were fatal, resulting in the deaths of 67 people, including spectators listed for this aircraft type at Aviation-Safety.
As far as aerobatic flying is concerned, you can refer to this article for an overview of aerobatic safety. Most accidents took place during airshows rather than during training.
Below is the NTSB's summary of aerobatic mishaps from 2008 - 2015.

The question asked for statistics, do you have any basis for your opinion? If not this would be better expressed as a comment.

For anyone who wonders, like I was, what the deal is with the huge outlier in 2011, this seems to be related to the Reno Air Races Crash (https://en.wikipedia.org/wiki/2011_Reno_Air_Races_crash)

Again, my inner lawyer comes out, and I would have to say well it depends.
Aerobatic flights like the ones listed there are going to be done with a competent aerobatic pilot at the controls in an airplane specifically designed and certified in the aerobatic category. This environment is also going to be further enhanced by flying at higher altitudes as required by government regulations in air space we’ll clear of airways and that is not high density traffic.  Use of parachutes and bail out procedures in case of trouble helps as well. The short and short of this is that the flight listed there would be pretty safe, if probably physically exhausting and/or nausea inducing for neophytes.
Aerobatics in general have a pretty good safety record associated with them despite requiring no official ratings - at least in the USA - to fly them.  Most people have followed the rules and lived.  The usual causes of aerobatic accidents are idiots doing things they shouldn’t do in planes that weren’t designed for it.  The aggressive hedge fund manager in his new SR22 does a few aileron rolls then attempts to do one at low level.  The airplane sinks rapidly while inverted and the haughty pilot can’t cope with the situation.  The last thing he sees is a dirt berm filling the windshield while he panics, hauling hard on the side yoke and can’t understand why the airplane is shaking and not responding.
The big elements that mean the difference between a safe ride and a dangerous one when doing aerobatics are:

Doing them in an aircraft certified in the aerobatic category, properly maintained, preflighted and loaded IAW the AFM.

An experienced and properly instructed aerobatic pilot at the controls.  If you’re a new pilot going out to try aerobatics with no formal training or forethought, you’re probably swimming in dangerous waters.

Flying maneuvers or maintaining load factors within those specifically approved for that airplane in the AFM.  Leave experimenting to the professionals.

Obey the regulations concerning aerobatic flight e.g. §91.303, etc.  Impulsivity, invulnerability, and machismo will get you killed.  Do not drink, smoke, or use drugs prior to an aerobatic flight.

Do not attempt aerobatic maneuvers without quality and competent instruction.  It invariably leads to poor and sometimes fatal outcomes.

Be acutely aware of your energy state prior to committing to downlines, particularly at low altitudes.  This is dramatically affected by high field elevations and density altitudes.  Have backup plans and alternatives if you don’t have the minimum energy and airspeed to commit.  Failure to do so is invariably fatal.

Don’t show off or hot dog; it’s a great way to dig a hole halfway to China.

Start high, work progressively lower when you can dependably avoid violating a pre-set hard deck.

Know your emergency and/or bail-out procedures down pat.  Always have contingency plans ready in case things go wrong.

Nothing listed there is extreme. However, IMO, a pilot with aerobatic experience is a SAFER pilot, because they have developed a greater sense of spatial awareness, a greater sense for the limits of the airplane, and knowledge of maneuvers that they can use to get out of bad situations. While accidents do happen, they are rare, and aerobatic pilots receive special training. They wouldn't be allowed to fly if they couldn't fly safely.


text:
Is there a VFR mobile app that shows other aircraft in real time?
In the UK, are there any apps available that show a real time radar / GPS of other aircraft and ideally their callsign?
As I fly Microlights, I only fly VFR, but in a high wing and often with low cloud, it's too easy not to spot others and would be much easier / safer if there was an app that handled this.

This is like my absolute sweet spot of question :) I could chat for hours about VFR tech! Give me a shout if you want to know more.

Wonderful! Thanks for the great answer, will investigate them and decide on one! I like that SkyEcho horizon and PFD that makes it look like you're flying a 737 ;)

I wonder: Do you want to look at such app while flying VFR? For what purpose exactly? I think such app may be useful outside of planes or for passengers, but not for pilots during flight, except maybe if you have an instrument failure. However think: Where do such apps get their data? Via mobile internet, most likely. Will it be available during the whole flight?

The most commonly used moving map GPS app in the UK for VFR flight is SkyDemon which is an absolutely incredible application written by what I consider to be geniuses. You really cannot get better. A close second is probably RunwayHD.
If you pair either of these apps with an electronic conspicuity device such as Rosetta Pilotaware or SkyEcho, then your moving map shows some (but crucially not all) other air traffic. Sometimes this is because of the differing technology, other times its due to capability of the device, and then there is interference between the big metal box you're in and the receiving/transmitting antennae.
Functionality varies between pilotaware and skyecho, and it's a bit of a VHS vs Betamax fight right now. You can hedge your bets on one, or wait until the fight is won. But neither device will ever be a complete replacement for the Mk1 eyeball. Traffic separation will always be your responsibility as PIC of a VFR aircraft.
It's also worth mentioning that the CAA is still doing a rebate scheme on EC devices as they have stated that they would like all aircraft to be carrying one. https://www.caa.co.uk/general-aviation/aircraft-ownership-and-maintenance/electronic-conspicuity-devices/

I like SkyDemon, it's a really well designed app. I'm of two minds whether to plug traffic data into it though. Technology is already causing too much head-down in the cockpit, I'd rather pilots were looking out than getting fixated on screens.

@GdD aha - thats where bluetooth equipped headsets come in. It talks to me to tell me where to point my Mk1 eyeballs. But saying that you're of course 100% right. Eyes outside not in the cockpit

What does Mk1 mean?

@Someone https://www.urbandictionary.com/define.php?term=Mk1%20eyeball

The free SafeSky app does exactly this. It's very popular in France (where it's from) and is gaining traction in other countries as well.

It shows data from other SafeSky users but also from all other traffic information sources (ADS-B, FLARM, MODE-S...) that are picked up by ground stations.
Of course it can't be 100% accurate and requires at least an EDGE cellular connection. So it's still your responsibility as PIC to be on the lookout.

Disclaimer: I'm not affiliated with SkySafe. I just think it's awesome

I've been keeping an eye on this, it is indeed getting some traction. From experience, I get a pretty good cell signal at 2000ft, but much higher I get nothing.

Ultimately, those tools are mostly useful when around airfields or at low altitude, when traffic is dense. When cruising, PIC's eyes with the assistance of Flight Information / Flight Following works best!

They certainly are useful around airfields, but in certain areas enroute (a number of which I could name off the bat) an extra pair of digital eyes is absolutely beneficial.

The high end Sentry receiver includes a FLARM chip, so no internet required.

It should be mentioned that supposedly you should not use cell-phones when flying. They are said to create problems for the cell phone network when one phone connects to several base stations normally out of sight. Other possible problems is when you receive a call on short final (happened to me) or when you place it next to the magnetic compass (been there as well).

@ghellquist don't worry, the carrier network will be just fine. For the call issue, one can always enable "Do not disturb" mode and be done with it. And for the compass, just put it far enough as you would do with any metallic/magnetic/electronic object that you may have to put somewhere on the dashboard. But this is a good point. One has to make sure the compass is OK before taking off!

@Jamiec are there any devices that allow mobile signal to work above 2k ft? Some kind of mobile satellite internet device or something?

@Cloud not that I know of

@cloud that could be a great question to ask so the technicalities of why it doesn't work can be answered.

Captain obvious here! Whichever app you choose to use, it absolutely does not diminish the necessity to scan the surroundings and monitor radio(s) at all, and it should not completely remove the anxiety about other traffic and all things flying in general.
As stated in the other answers, none of the apps can provide 100% coverage of other traffic, and as such may provide false sense of security.
Should you choose to use one (and I recommend you should, despite this "rant"), make sure you learn and use proper scanning technique, maintaining your main focus on the surroundings of the aircraft, not the inside.

If you have an Android device with gps, or an external gps, Avare provides a glass cockpit type moving map experience. If you add a pair of rtl sdr it will also plot other planes with ADS Mode C and I'm pretty sure Mode S. I haven't looked lately to see if it has added support for TCAS. The thing you wont get without internet is plane type descriptions since that is provided from database lookups of the tail number sent as part of the ads message.
You can download all of the charts you need (at least in the US) and fly without needing internet.
The ideal setup is a battery pack with a USB-C hub and PD for your device that has USB-A ports for the rtl devices. That way it can be stand alone from the aircraft electronics.